The studies are to be carried out on the effects of androgens on CNS differentiation and on gonadotrophin regulation in the differentiated organism. With respect to CNS differentiation, the aim is to try to pinpoint the time of onset in the normal rat of the process of androgen dependent neuronal changes, to identify the cell populations affected and to trace the biochemical consequences of the action of testosterone on these cell populations. The RNA content and aromatizing potential of identified limbic system nuclei will be measured in rat fetuses from day 16 of gestation through day 1 postnatally using micro-analytical and quantitative cytochemical techniques. Studies will be carried out also to try to identify the mechanisms by which stressing pregnant rats lowers androgen levels in the fetus and causes abnormal behavioral differentiation. Gonadotrophin regulation will be studied in the perifused anterior pituitary and medial-basal hypothalamus of the rat. The mechanism of the acute effects of androgens on pituitary responsiveness to Gn-RH will be studied and attempts made to identify the neurotransmitter (s) responsible for normal Gn-RH release. Studies of the normal process of masculinization of brain should ultimately provide the basis for helping to prevent abnormalities in sexual differentiation of brain from developing in the human fetus. Knowledge of the central mechanisms regulating gonadotrophin secretion provides the basis for helping infertile human subjects and for anticipating untoward consequences of contraceptive agents.